the major commercial aluminium ore is bauxite,AlO3.H2O(s).What is its molar mass?The analysis of a representive sample of bauxite shows it contains 70% by mass of Al2O3..What is the maximum mass of aluminium metal that could be obtained from 200kg of bauxite by the HAll electrolytic process?

Here is a sample problem I posted for stoichiometry. Use that as a guide. Most of these are worked about the same way. The starting mass will be 200,000 x 0.92 = ?? g Al2O3. I expect your book has the equation for the electrolysis of bauxite by the Hall process.